Molar Enthalpy Change Research Articles

Solubility enhancement of metronidazole using natural deep eutectic solvents: Physicochemical and thermodynamic studies

This research aimed to explore the utility of natural deep eutectic solvents (NADES) as the co-solvents for slightly water-soluble metronidazole (MNZ). After testing 70 wt% (percentage by weight) aqueous mixtures of seven NADESs, it was found that MNZ had the highest solubility in water solutions of NADES composed of choline chloride (ChCl) and citric acid (CA). The solubility of MNZ (expressed as 103 mol fraction) increased with the concentration of ChCl:CA NADES (from 6.7743 to 26.8518 at 298.5 K, for 30 and 70 wt% NADES-water mixtures, respectively), and it was more effective when compared to aqueous solutions of individual NADES components with wt% corresponding to these in the NADES-water mixtures. The study also found a preferable mixing of MNZ with aqueous solutions of NADES reflected by negative values of standard molar enthalpy change of mixing (approx. − 4.2 kJ·mol−1), compared with positive values in the case of MNZ mixing with water or ChCl aqueous solutions (approx. 7.3 kJ·mol−1). Comparative research conducted on the volume and acoustics of MNZ in water and aqueous solutions of ChCl, CA, and ChCl:CA NADES also confirmed stronger interactions between the drug and NADES and CA. The dominant interactions between MNZ and co-solvent were hydrophilic-hydrophobic and hydrophobic-hydrophobic. This effect increased in the following strength order: ChCl < NADES < CA. In conclusion, the obtained NADES seems to be a promising co-solvent which provides solid grounds for further research to evaluate the full potential in pharmaceutical design of MNZ liquid formulations.

Reaction of KHP with excess NaOH or TRIS as standard reactions for calibration of titration calorimeters from 0 to 60°C.

Calibration of titration calorimeters is an ongoing problem, particularly with calorimeters with reaction vessel volumes < 10 mL in which an electrical calibration heater is positioned outside the calorimetric vessel. Consequently, a chemical reaction with a known enthalpy change must be used to accurately calibrate these calorimeters. This work proposes the use of standard solutions of potassium acid phthalate (KHP) titrated into solutions of excess sodium hydroxide (NaOH) or excess tris(hydroxymethyl)aminomethane (TRIS) as standard reactions to determine the collective accuracy of the relevant variables in a determination of the molar enthalpy change for a reaction. KHP is readily available in high purity, weighable for easy preparation of solutions with accurately known concentrations, stable in solution, not compromised by side reactions with common contaminants such as atmospheric CO2, and non-corrosive to materials used in calorimeter construction. Molar enthalpy changes for these reactions were calculated from 0 to 60°C from reliable literature data for the pKa of KHP, the molar enthalpy change for protonation of TRIS, and the molar enthalpy change for ionization of water. The feasibility of using these reactions as enthalpic standards was tested in several calorimeters; a 50 mL CSC 4300, a 185 μL NanoITC, a 1.4 mL VP-ITC, and a TAM III with 1 mL reaction vessels. The results from the 50 mL CSC 4300, which was accurately calibrated with an electric heater, verified the accuracy of the calculated standard values for the molar enthalpy changes of the proposed reactions.

Deciphering the spectroscopic and thermodynamic aspects of binding of biologically important antioxidants with the alkali induced state of human serum albumin.

Protein-ligand interactions are crucial for developing and identifying novel therapeutic targets. In this study, we investigate the interaction of the alkali induced state of human serum albumin (pH 11.2) with three hydroxycinnamic acid derivatives (HCDs), ferulic acid (FA), sinapic acid (SA) and trans-o-coumaric acid, which are biologically important antioxidants, and compare the outcomes with the results obtained at physiological pH (7.4). This study aims to explore the interaction of altered protein conformation with small molecules. Spectroscopic characterization methods show that the conformation of HSA and the ionic properties of HCDs are pH-dependent. Fluorescence, FRET and lifetime measurements reveal that the binding of HCDs with HSA is different at both pH 7.4 and 11.2. Despite the moderate binding of HCDs to HSA, circular dichroism and thermal denaturation studies report no conformational changes in HSA in the presence of HCDs. Isothermal titration calorimetry is employed to assess their binding based on structure and energetics using thermodynamic parameters. Standard molar enthalpy change (ΔH0m) and standard molar entropy change (ΔS0m) values vary with the change of pH from 7.4 to 11.2 with the contributions from the exothermicity and hydrophobicity of functional and aromatic groups of HCDs. Ferulic acid (FA) and sinapic acid (SA) binding to HSA is entropically driven, whereas trans-o-coumaric acid (CA) acid binding is enthalpically favourable. Our ITC studies also reveal that the involvement of -OH functional groups present in CA in binding with HSA is greater than that present in FA and SA at pH 11.2. Overall, this experimental study shows the comparable binding strength of HCDs to both the alkali-induced state of HSA and native HSA (pH 7.4). However, the mechanism of their binding is different.

Binding Thermodynamics of Ferrocenyl Ammoniums by Sulfonated Calix[4]arenes

AbstractThe binding constants (Ka), standard molar enthalpy changes (ΔH°), and entropy changes (TΔS°) between two sulfonated calix[4]arene hosts including rigid p‐sulfonatocalix[4]arene (SC4A) and flexible p‐sulfonatothiacalix[4]arene (STC4A), and three ferrocenyl ammonium guests modified by different aliphatic chains were determined in aqueous solution (pH 7.0 and pH 2.0) by isothermal titration microcalorimetry (ITC). The gained data indicated that for the flexible host STC4A, the host‐guest binding affinities increased with the increase of length of the aliphatic chain of guests whereas the rigid host SC4A behaved almost oppositely. Compared with those at pH 2.0, the binding affinities between the hosts and the guests were much stronger at pH 7.0. This should be attributed to the higher π‐electron density and the extra negative charge of calixarene cavities owing to one of the phenolic hydroxyl groups is deprotonated at pH 7.0, thus affording stronger π⋯π, C−H⋯π and electrostatic interactions. Job plot and ITC confirmed that the molecular binding were stoichiometric 1 : 1 between hosts and guests. NMR experiments showed that the signals of the guest protons with addition of hosts underwent pronounced upfield shifts suggesting the effective binding between hosts and guests. In addition, the molecular selective binding behavior was discussed from the perspective of thermodynamics.

Solubility Measurement and Data Correlation of Cyclohexanone, tert-Butanol, and 1,4-Dioxane in p-, o-, and m-Xylenes and Ethylbenzene

The solubility of cyclohexanone, tert-butanol, and 1,4-dioxane in p-, o-, and m-xylenes and ethylbenzene was measured by a gas chromatography method under an atmospheric environment. The measured data indicated that the solubility of cyclohexanone, tert-butanol, and 1,4-dioxane in the xylenes and ethylbenzene increases with increasing temperature. The experimentally determined solubility results were fitted with the modified Apelblat equation, Van’t Hoff equation, and Wilson model. Among them, the Wilson model was most consistent with the measured solubility results. The dissolution-related thermodynamic properties of cyclohexanone, tert-butanol, and 1,4-dioxane in xylenes and ethylbenzene, including the changes of molar Gibbs free energy, molar enthalpy, and molar entropy, were predicted and analyzed via the correlated Wilson model, which indicates that the dissolution behaviors are spontaneous and endothermic process. The obtained solubility results provide the thermodynamic foundation for the development and upgrading of industrial separation processes related to xylene, ethylbenzene, cyclohexanone, tert-butanol, and 1,4-dioxane.

Experimental and Computational Characterisation of the Molecular Interactions between 1‐Butyl‐1‐methyl‐pyrrolidin‐1‐ium bis(trifluoromethanesulphonyl)imide and Human Serum Albumin

AbstractRecently, ionic liquids (ILs) have emerged as a therapeutic agent for industrial‐based pharmacology. In this regard, the current study highlights the key aspects of IL, (1‐butyl‐1‐methyl‐pyrrolidine‐1‐ium bis(trifluoromethanesulphonyl)imide), [Pyr C4 NTf3−] such as pharmacodynamics and pharmacokinetics. We performed a detailed experimental and computational analysis of [Pyr C4 NTf3−] with human serum albumin (HSA) using various spectroscopic techniques viz. UV‐vis, steady‐state fluorescence, synchronous fluorescence, time‐resolved fluorescence, steady‐state anisotropy and tensiometry study along with molecular docking. Absorption and emission spectral studies revealed the complex formation between [Pyr C4 NTf3−] and HSA where the binding constant (Kb) was found to be 5.5×103 Lmol−1. Thermodynamic parameters, Gibb's free energy change (ΔG), molar enthalpy change (ΔH), and molar entropy change (ΔS) revealed that the complex formation process is spontaneous, and enthalpy driven where involvement of hydrogen bond and van der Waal forces play a major role. Further, CD spectroscopy and ANS experiment showed the stability of HSA in presence of [Pyr C4 NTf3−]. A site marker study suggested that the binding of [Pyr C4 NTf3−] occurred at site II in HSA which is well supported by a molecular docking study. Also, MD simulation was done which revealed the stability of the complex formed between HSA and [Pyr C4 NTf3−]. The study might help in utilizing [Pyr C4 NTf3−], IL as a therapeutic agent in the pharmaceutical industries.

Solubility measurement, correlation, and dissolution thermodynamics of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane · 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (2HNIW·HMX) co-crystal in two binary solvent mixtures

The solubility of 2HNIW·HMX co-crystal in two binary solvent mixtures (ethanol + methyl acetate, and 1,2-dichloroethane + methyl acetate) was measured by gravimetric method at various temperatures (283.15, 288.15, 293.15, 298.15, 303.15, 308.15, 313.15 and 318.15 K) under atmospheric pressure (0.1 MPa). The experimental results revealed that the solubility for co-crystal in binary solvent mixtures is a simple function of ethanol (or 1,2-dichloroethane) mass fraction and temperature, which decreased with increasing temperature and mass fraction of ethanol (or 1,2-dichloroethane) in the binary solvent mixtures. The solubility of 2HNIW·HMX co-crystal was correlated with the modified Apelblat equation, CNIBS/R-K model, Jouyban-Acree-van't Hoff model, and Jouyban-Acree-Apelblat model. The fitting results demonstrate that the modified Apelblat model and CNIBS/R-K model provided a better correlation with the experimental results than the other models. Furthermore, the van’t Hoff equation was used to study the thermodynamic properties of the 2HNIW·HMX co-crystal dissolution process, including the apparent molar enthalpy change (ΔdisH°), the apparent molar entropy change (ΔdisS°), and the apparent molar Gibbs free energy change (ΔdisG°). The results show that the dissolution of the co-crystal in the selected binary solvent mixture is an exothermic process. The experimental and calculated solubility data and thermodynamic properties of the 2HNIW·HMX co-crystal would be helpful for selecting the appropriate solvent system for the reaction, crystallization, and purification of the 2HNIW·HMX co-crystal.

DFT Study of the Possible Reaction Path for Radical Promoted Esterification Mechanism of Free Fatty Acids of Soapnut Oil for the Production of Biodiesel

Abstract:Esterification of higher free fatty acids content by using a photo-catalyst has recently been proved as the most efficient method for the pretreatment of non-edible oil to synthesize biodiesel.Methods:In the current study, mechanistic details of photo-catalyzed esterification reaction for four different fatty acids through density functional theory (DFT) calculations are explored and compared with un-catalyzed esterification reaction.Results:Revealed that the presence of photo-catalyst lowers the activation barrier and the structure of fatty acid has no significant effect on its reactivity. Thermodynamic data also revealed that the presence of photo-catalyst lowered the activation energy from 51.67 kcal/mol to 0.7495 kcal/mol. Furthermore, Gibbs free energy changes (ΔrGm Ø) and molar enthalpy changes (ΔrHm Ø) of the photo-catalyzed esterification reaction are negative, indicating that it is a spontaneous exothermic reaction. On the other hand, free fatty acids esterification in the absence of a catalyst is a kinetically unfavorable process with positive values of ΔrGm Ø and ΔrHm Ø.Conclusion:Our findings theoretically clarify the mechanism of the photo-catalyzed esterification reaction of FFA present in non-edible oil, which facilitates the process of biodiesel production.

GCMC simulation of supercritical N&lt;sub&gt;2&lt;/sub&gt; adsorption in single-walled carbon nanotubes

The development of supercritical fluid technology is becoming more and more mature. The research on the adsorption behaviors of supercritical fluid in nanoporous materials has theoretical significance and application value for the development and application of supercritical fluid technology. In this paper, the grand canonical Monte Carlo (GCMC) method is used to simulate the adsorption behaviors of N&lt;sub&gt;2&lt;/sub&gt; in single-walled carbon nanotubes under supercritical condition and subcritical condition, and the isosteric heat of adsorption and integral molar enthalpy change in different adsorption systems are discussed. The results show that the adsorption isotherms of N&lt;sub&gt;2&lt;/sub&gt; in SWCNT do not strictly follow the layered adsorption mechanism under supercritical condition, as a result of the increase of molecular thermal motion, the degree of free mobility becomes higher, and it is easier for nitrogen molecule to intersperse and jump between different molecular layers. The nitrogen adsorption isotherm has a peak, which decreases gradually with the increase of temperature, while the critical pressure at peak increases with the temperature increasing. Around the critical point temperature (126 K), a small change in pressure can cause large fluctuations in the bulk gas phase density, resulting in a sharp drop in the adsorption isotherm after peaking. What is different from the subcritical condition is that the adsorption peak of local density distribution curve of the fluid under supercritical condition cannot represent the increase of excess adsorption capacity, and the influence of gas phase density on the adsorption process cannot be ignored. By studying the adsorption integral molar enthalpy under the supercritical condition, it is found that the excess integral molar enthalpy decreases with the pore size increasing; the adsorption integral molar enthalpy decreases with the augment of pore size at lower pressure, but due to a fact that the proportion of gas phase fluid in large-pore SWCNTs increases at higher pressure, on the contrary, it increases with the pore size at higher pressure increasing.

Solutions, in Particular Dilute Solutions of Nonelectrolytes: A Review

The liquid state is one of the three principal states of matter and arguably the most important one; and liquid mixtures represent a large research field of profound theoretical and practical interest. This topic is of importance in many areas of the applied sciences, such as in chemical engineering, geochemistry, the environmental sciences, biophysics and biomedical technology. First, I will concisely present a review of important concepts from classical thermodynamics of nonelectrolyte solutions; this will be followed by a survey of (semi-)empirical approaches to representing the composition and temperature dependence of selected thermodynamic mixture properties, and finally the focus will be on dilute binary nonelectrolyte solutions where one component, a supercritical solute, is present in much smaller quantity than the other component, called the solvent. Partial molar properties in the limit of infinite dilution (indicated by a superscript ∞) are of particular interest. For instance, activity coefficients (Lewis–Randall (LR) convention) are customarily used to characterize mixing behavior, and infinite-dilution values gamma_{i}^{{{text{LR,}}infty }}provide a convenient route for obtaining binary parameters for several popular solution models. When discussing solute (j)—solvent (i) interactions in solutions where the solute is supercritical, the Henry fugacity h_{j,i} left( {T,P} right), also known as Henry’s law (HL) constant, is a measurable thermodynamic key quantity. Its temperature dependence yields information on the partial molar enthalpy change on solution Delta H_{j}^{infty } left( {T,P} right), while its pressure dependence yields information on the partial molar volume V_{j}^{{{text{L,}}infty }} left( {T,P} right) of solute j in the liquid phase (superscript L). I will clarify issues frequently overlooked, touch upon solubility data reduction and correlation, report a few recent high-precision experimental results on dilute aqueous solutions of supercritical nonelectrolytes, and show the equivalency of results for caloric quantities (e.g. Delta H_{j}^{infty }) obtained via van ’t Hoff analysis of high-precision solubility data with directly measured calorimetric data.

Polymer-Surfactant Driven Interactions and the Resultant Microstructure in Protein-Containing Liquid Crystal Droplets.

Integration of molecular liquid crystals (LCs) with functional proteins can provide new class of materials for potential applications in optical biosensing. However, hydrophobic nematic LCs (length ∼ 1-2 nm) and hydrophilic proteins, size ∼ O (nm), do not intermix without chemical modification of at least one of them. Bioconjugation of proteins with a polyethylene glycol-based polymeric surfactant (PS) can provide a core-shell system that is sequestered within nonaqueous LC (4-cyano-4'-pentylbiphenyl) microdroplets. However, the nature of interactions between the components and detailed understanding of the resultant hybrid microstructure remains unclear. Here, using a combination of isothermal titration calorimetry (ITC), fluorescence microscopy, and infrared-imaging spectroscopy, we show that strong hydrophobic interactions between the LC and PS drives the sequestration of a myoglobin-PS (Mb-PS; dispersed in the aqueous phase) into the LC spherical microdroplets or even into a bulk LC phase. The average values of both, the binding constant and the standard molar enthalpy change, are increased by approximately a factor of 2.5 times when the unmodified Mb is conjugated to the PS. Small-angle X-ray scattering studies reveal that LC molecules act as a solvent for the Mb-PS conjugate; furthermore, the LC long-range order is disturbed due to mixing, as exemplified by the change in its coherence length from 8.9 to 5.7 nm. Detailed all-atomistic molecular dynamic simulations for a three-component PS-water-LC system show a change in interaction energy of -144 kJ mol-1 PS-1 upon the contact of PS chains (initially dispersed in water) with LC and agree with the ITC experiments.

Investigation on conformational variation and fibrillation of human serum albumin affected by molybdenum disulfide quantum dots

In this work, binding interaction between molybdenum disulfide quantum dots (MoS2 QDs) and human serum albumin (HSA) was researched deeply to dissect the conformational variation and fibrillation of HSA affected by MoS2 QDs. The results revealed that MoS2 QDs bound strongly with HSA with molar ratio of 1:1 under the joint actions of hydrogen bond and van der Waals force, leading to the static fluorescence quenching of HSA. MoS2 QDs caused the secondary structure transition of HSA from α-helix stepwise to β-turn, β-sheet, and random coil gradually. MoS2 QDs reduced both the molar enthalpy change and the melting temperature of HSA, reducing the thermal stability of HSA significantly. It is worth noting that MoS2 QDs inhibited the fibrillation process of HSA according to the reduced hydrophobic environment and the disturbance of disulfide bonds in HSA network structure. These results reveal the precise binding mechanism of MoS2 QDs with HSA at molecular level, providing indispensable information for the potential application of MoS2 QDs in biological fields.

Computational design and screening of promising energetic materials: The coplanar family of novel heterocycle‐based explosives

AbstractA series of coplanar compounds based on triazine ring and triazole ring are proposed for the design of new energetic materials. The molecular structure, electronic structure, stability and detonation properties of these 40 compounds have been calculated by the density functional theory method. With the participation of hydroxyl, amino and nitro groups, these nitrogen‐rich fused ring compounds have the characteristics of aromaticity and hydrogen bonding. At the same time, the standard molar heat capacity, standard molar entropy and standard molar enthalpy change trends of some representative compounds in the temperature range of 200–800 K were calculated. The detonation performance, stability and density of these coplanar compounds were compared. There are 25 compounds with high density (ρ = 1.80–1.94 g·cm−3), of which A3‐2 exhibits excellent detonation performance (ρ = 1.93 g·cm−3, D = 8.86 km·s−1, P = 36.27 GPa), it is a potential candidate for high energy density materials. These research results provide a theoretical basis for the future design and screening of new energetic materials.

Solubility Measurements and Thermodynamic Properties of Sorbic Acid in Binary Solvent Mixtures of (Ethanol, 1-Propanol or 2-Propanol + Water) from 283.15 to 323.15 K

The solubility data of sorbic acid in binary systems of (ethanol + water), (1-propanol + water) and (2-propanol + water) were measured from 283.15 to 323.15 K using the static equilibrium method under atmospheric pressure. It was found that the solubility of sorbic acid in the three binary solvent systems increased with increasing temperature as well as increasing initial mole fraction of organic solvent in these systems. The van’t Hoff–Jouyban–Acree model, the modified Apelblat–Jouyban–Acree model and the CNIBS/R-K model were proposed for correlating the experimental solubility values in various solution systems. Furthermore, the dissolution thermodynamic properties of Gibbs energy change (ΔsolGo), molar enthalpy change (ΔsolHo) and molar entropy change (ΔsolSo) were calculated from the experimental solubility data, using the van’t Hoff equation. The positive values of ΔsolGo, ΔsolHo and ΔsolSo indicate that these dissolution processes of sorbic acid in the solvents studied were all endothermic and entropically favorable. In addition, the change of dissolution enthalpy was the main contributor to the positive value of the molar Gibbs energy of the dissolution process. The experimental solubility and the models used in this work would be conducive to purifying sorbic acid from its crude mixtures.

Measurement and correlation of solubility of HNIW·TNT co-crystal in (methanol/1,2-dichloroethane + ethyl acetate) solvent mixtures from 283.15 to 318.15 K

The solubility of HNIW·TNT co-crystal was experimentally measured by a gravimetric method in (methanol + ethyl acetate) and (1,2-dichloroethane + ethyl acetate) solvent mixtures at the temperature range from 283.15 to 318.15 K under atmospheric pressure (p = 0.1 MPa). The measured results indicate that the solubilities of HNIW·TNT co-crystal were significantly affected by the temperature and the mole fraction of methanol or 1,2-dichloroethane. Within the range of the molar fraction of methanol and 1,2-dichloroethane, the average solubilities of HNIW·TNT co-crystal in the corresponding binary solvent mixtures decreased from (7.63 × 10−2) to (0.82 × 10−2, 7.66 × 10−2) to (1.75 × 10−2), respectively. The modified Apelblat equation, the CNIBS/R-K model, the Van't Hoff-Jouyban-Acree model, and the Apelblat-Jouyban-Acree model were successfully used to correlate the experimental solubility of HNIW·TNT co-crystal, and the calculated solubility data are good agreement with the experimental data. In addition, the calculated values of the molar enthalpy change (∆solH°) and the Gibbs free energy change (∆solG°) indicated that the dissolution behavior of HNIW·TNT co-crystal in the solvent mixtures is endothermic and not spontaneous. In this work, the experimental solubility and correlation equations, as well as the thermodynamic parameters of HNIW·TNT co-crystal during the dissolution process were obtained, which would be useful for facilitating the industrial crystallization process of HNIW·TNT co-crystal and further theoretical studies.

Thermodynamic modelling, Hansen solubility parameter and solvent effect of oxaprozin in thirteen pure solvents at different temperatures

The solubility of oxaprozin in thirteen organic solvents (methanol (MeOH), ethanol (EtOH), n-propanol (n-PrOH), n-butanol (n-BuOH), n-pentanol (n-PeOH), methyl acetate (MeAC), ethyl acetate (EtAC), n-propyl acetate (n-PrAC), n-butyl acetate (n-BuAC), n-amyl acetate (n-AmAC), N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO)) was determined using a laser monitoring method at atmospheric pressure in this work. The measured temperature range for all selected solvents is 278.15 K to 323.15 K except DMSO 293.15 K to 323.15 K. Through the entire studied temperature range, the results turned out that oxaprozin solubility in selected solvents has a positive correlation with temperature variation. Four mathematical models were employed to correlate the solubility data including two empirical models (modified Apelblat model, λh model) and two activity coefficient models (UNIQUAC model, NRTL model), with the modified Apelblat model giving the best regression. Solubility order of oxaprozin in thirteen solvents was analysed by using the Hansen solubility parameter (HSP) and the solvent effect (solvent interaction) was investigated through correlating oxaprozin solubility in selected solvents based on KAT-LSER model. Moreover, according to van’t Hoff equation, thermodynamic properties including apparent standard molar enthalpy change (ΔsolH °), apparent standard molar Gibbs energy change (ΔsolG°) and apparent standard molar entropy change (ΔsolS) of the dissolution process of oxaprozin were also calculated and discussed.

Utilization of Biomass Fly Ash for Improving Quality of Organic Dye-Contaminated Water.

Development of innovative methodologies to convert biomass ash into useful materials is essential to sustain the growing use of biomass for energy production. Herein, a simple chemical modification approach is employed to functionalize biomass fly ash (BFA) with 3-aminopropyltriethoxy silane (APTES) to develop an inexpensive and efficient adsorbent for water remediation. The amine-functionalized BFA (BFA–APTES) was fully characterized by employing a range of characterization techniques. Adsorption behavior of BFA–APTES was evaluated against two anionic dyes, namely, alizarin red S (ARS) and bromothymol blue (BTB). In the course of experimental data analysis, the computation tools of data fitting for linear and nonlinear form of Langmuir, Freundlich, and the modified Langmuir–Freundlich adsorption isotherms were used with the aid of Matlab R2019b. In order to highlight the misuse of linearization of adsorption models, the sum of the squares of residues (SSE) values obtained from nonlinear models are compared with R2 values obtained from the linear regression. The accuracy of the data fitting was checked by the use of SSE as an error function instead of the coefficient of determination, R2. The dye adsorption capacity of BFA–APTES was also compared with the nonfunctionalized BFA. The maximum adsorption capacities of BFA–APTES for ARS and BTB dye molecules were calculated to be around 13.42 and 15.44 mg/g, respectively. This value is approximately 2–3 times higher than the pristine BFA. A reasonable agreement between the calculated and experimental values of qe obtained from the nonlinear form of kinetic models verified the importance of using equations in their original form. The experimentally calculated thermodynamic parameters including molar standard Gibbs free energy (ΔadGm0) and molar standard enthalpy change (ΔadHm0) reflected that the process of adsorption of dye molecules on the BFA–APTES adsorbent was spontaneous and exothermic in nature. Moreover, the used BFA–APTES adsorbent could be regenerated and reused for several cycles with significant dye adsorption capacity. The remediation capability of the BFA–APTES adsorbent against ARS dye was also demonstrated by packing a small column filled with the BFA–APTES adsorbent and passing a solution of ARS through it. Overall, we provide a simple and scalable route to convert BFA into an efficient adsorbent for water remediation applications.

Low-temperature heat capacity of d-glucose and d-fructose

The thermodynamics data of crystalline states of two representative components in blood sugar, d-glucose and d-fructose, are significant in researching artificial synthesis and composition transformation in vivo. The heat capacities of d-glucose and d-fructose over a temperature range of 1.9–300 K were measured and calculated by the heat capacity measurement module of physical property measurement system (PPMS). The heat capacities of two compounds increased steadily with temperature, showing a smooth curve without any thermal anomalies. The heat capacity of d-glucose is greater than that of d-fructose in the range of 0 K < T < 80 K, which is smaller than that of d-fructose between 80 and 300 K. Based on the lattice vibration mode, factors of generating the difference heat capacity data between the two isomers were investigated. Additionally, the heat capacity data were fitted by low-temperature heat capacity theoretical model. The thermodynamic data that molar entropy change and molar enthalpy change over the temperature range of 0–300 K were calculated. The standard molar entropy of d-glucose and d-fructose at 298.15 K was calculated by heat capacity fitting to be 214.64 and 217.56 J K−1 mol−1, all with an error of 0.21.

Sharp difference in the change in molar volumes and enthalpy of dissolution of 2D and 3D molecules in solvents illustrated by the Diels-Alder reaction

A sharp difference in the change in the molar volume during the transition from the solid phase to the solution for a number of 2D molecules of reagents compared with 3D molecules of the Diels-Alder reaction adducts was observed. The dissolution of 2D crystal molecules is accompanied by a significant increase in volume (10–15%) with a dissolution enthalpy close in magnitude to the fusion enthalpy. A similar transition for 3D crystal molecules is often accompanied by an unexpected decrease in volume and even negative enthalpy of dissolution in inert solvents. The similar change in these parameters is also considered for a number of 3D molecules: 1,3,5-triphenylbenzene, hexaphenylbenzene, 9,10-diphenylanthracene, congressane, and C-60 fullerene. This can be explained by the fact that the surface of large 3D molecules in a solution can be much more thoroughly surrounded by solvent molecules than in its own environment. These results indicate that the values of activation and reaction volumes and their ratio (ΔV≠S/ΔVr-n, S) may be weakly related to the mechanism of non-polar cycloaddition reactions.

Betulin/2-hydroxypropyl-β-cyclodextrin inclusion complex: Physicochemical characterization and hepatoprotective activity

The thermodynamic and spectroscopic parameters of the betulin/2-hydroxypropyl-β-cyclodextrin (HPβCD) inclusion complex and its hepatoprotective activity were investigated in rats with nonalcoholic steatohepatitis (NASH). The pentacyclic triterpene betulin was isolated from birch bark and complexed with HPβCD. The parameters of inclusion complex formation were evaluated by infrared spectroscopy and differential scanning and isothermal titration calorimetries. The aqueous solubility and stability of betulin were significantly increased due to the formation of a stable inclusion complex with a stoichiometry of 1:1. The determined changes in molar enthalpy (ΔH < 0), entropy (ΔS > 0) and free energy (ΔG < 0) values indicate energetically favorable and spontaneous nature of the ligand-receptor interaction. The association constant of the betulin/HPβCD complex formation was equal to 1330 ± 111 M−1, as was determined by a calorimetric method. The complex formation was enthalpy and entropy driven. In rats with NASH induced by a high-fat diet, the oral administration of the betulin/HPβCD complex at 50 mg/kg betulin equivalent resulted in marked liver protective effects exceeding those of a higher dose (100 mg/kg) of betulin alone. Specifically, the betulin/HPβCD complex decreased lipid accumulation, the number of inflammatory foci in the liver, the activities of the serum marker enzymes, and the circulating TNFα level. Therefore, the complexation of betulin with HPβCD, improving aqueous solubility and, in turn, bioavailability, could be a prospective strategy to enhance antioxidative, anti-inflammatory, and hepatoprotective properties of betulin as a promising candidate for treatment of NASH.